The initiation of blood coagulation through the factor VII-Tissue Factor pathway is not only important for normal hemostasis, but likely plays a role in pathological thrombosis as well. Cellular expression of TF has been correlated with infectious, inflammatory, and neoplastic disease, and may be responsible in part for the thromboembolic complications of not only these illnesses, but also the venous thromboembolic and pulmonary embolism occurring in otherwise normal individuals as well. Plasma contains an endogenous inhibitor of the VII-TF complex which we call LACI. It is associated with the lipoproteins in plasma and requires the presence of Xa to express its feedback inhibition of VII-TF. We plan to further characterize LACI by isolating its cDNA, determining the spectrum and kinetics of its protease inhibition, and investigating the structure function relationships of the LACI molecule vis a vis its association with lipoproteins, its inhibition of Xa, and its relationship to the other components in the putative VII-TF-Xa-LACI inhibitory complex. Additional studies will also investigate the synthesis of TF and LACI by cells, determine the immunohistochemical localization of TF/LACI in normal and pathological tissues, and assess the relationship between TF and LACI blood concentrations and clinical disease. These studies will be performed using purified TF and LACI, fragments of them produced by proteolysis or chemical treatment (CnBr), their isolated cDNAs, synthetic peptides based on their predicted amino acid sequence, and appropriate monoclonal and polyclonal antibodies. The experiments are designed to provide information, now lacking, concerning the initiation and control of coagulation and the interrelationship between the classical "extrinsic" and "intrinsic" pathways. The results should enhance our understanding of both normal hemostasis and pathologic thromboembolism.